1. Antisera raised in mice against purified nuclear and cytoplasmic poly(A)-binding proteins have been used to isolate genes for these proteins from yeast. DNA sequence determination and mutational analysis of the genes are in progess. 2. Preliminary studies have demonstrated the capacity of synthetic peptides to serve as signal sequences for the transport of proteins by nuclear membranes. We propose to exploit this finding to isolate the nuclear signal receptor, determine its location in the nuclear envelope, isolate the gene for the receptor, and reconstitute the transport process in vitro.